Monthly Downloads: 1,878
Programming language: Elixir
License: MIT License
Tags: Testing    
Latest version: v4.5.0

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This project is looking for someone who'd like to take over ownershp: Discuss here: https://github.com/meadsteve/white-bread/issues/114


Story BDD tool written in and for Elixir. Based on cucumber. Parses Gherkin formatted feature files and executes them as acceptance tests.

Is this a testing tool?

The short answer is no. The medium answer is it's a development tool that should really be used in conjuction with some testing framework. For a longer answer checkout this post by Aslak Hellesøy: the world's most misunderstood collaboration tool.

Why the name?

Gherkin and cucumber made me think of cucumber sandwiches. Which are traditionally made with very thin white bread.

Alternative tools

Before adopting whitebread you should investigate the alternaitves. This project (whitebread) contains a lot of code around setup, execution, and output of tests. An alternative gherkin based BDD tool can be found at https://github.com/cabbage-ex/cabbage. Cabbage parses gherkin feature files and creates exunit tests. This means a lot more of the logic is standard exunit code.

Getting started - installing

Add "white_bread" to your mix.exs file with the version you wish to use:

defp deps do
        { :white_bread, "~> 4.1.1", only: [:dev, :test] }

Getting started - Basic usage

Create a features directory. In here add some *.feature files describing your software. They should be gherkin syntax like:

Feature: Serve coffee
  Coffee should not be served until paid for
  Coffee should not be served until the button has been pressed
  If there is no coffee left then money should be refunded

  Scenario: Buy last coffee
    Given there are 1 coffees left in the machine
    And I have deposited £1
    When I press the coffee button
    Then I should be served a coffee

Run the command:

mix white_bread.run

This should prompt you with a few messages like:

loading config from features/config.exs
Config file not found at features/config.exs.
Create one [Y/n]?

Suite: All
Context module not found Elixir.WhiteBreadContext (features/contexts/white_bread_context.exs)
Create one [Y/n]?

This will create a basic config file and also a context features/contexts/white_bread_context.exs. A context file tells WhiteBread how to understand the gherkin in your feature files and also what setup is required.

These will need to be implemented like:

defmodule SunDoe.CoffeeShopContext do
  use WhiteBread.Context

  feature_starting_state fn  ->
    coffee_storage = setup_coffee_storage
    %{in_memory_coffee_db: coffee_storage}

  scenario_starting_state fn state ->
    state.in_memory_coffee_db |> clear_db

  # `_status` will be either {:ok, scenario} | {:error, reason, scenario}
  scenario_finalize fn _status, state ->
    state.in_memory_coffee_db |> shutdown_db

  given_ "there are 1 coffees left in the machine", fn state ->
    {:ok, state |> Dict.put(:coffees, 1)}

  given_ ~r/^I have deposited £(?<pounds>[0-9]+)$/, fn state, %{pounds: pounds} ->
    {:ok, state |> Dict.put(:pounds, pounds)}

  when_ "I press the coffee button", fn state ->
    # Domain logic to serve coffees would happen
    # here. Then update the state with the result
    {:ok, state |> Dict.put(:coffees_served, 1)}

  then_ "I should be served a coffee", fn state ->
    served_coffees = state |> Dict.get(:coffees_served)

    # The context automatically imports ExUnit.Assertions
    # so any usual assertions can be made
    assert served_coffees == 1

    {:ok, :whatever}

After doing this rerun

mix white_bread.run

If you want to run WhiteBread in test environment run this

MIX_ENV=test mix white_bread.run

To execute on each time WhiteBread in test environment without prefixing the command with MIX_ENV=test, you can also add this line in mix.exs

def project do
        preferred_cli_env: ["white_bread.run": :test],

Integrating a testing library

By default, use WhiteBread.Context will import ExUnit.Assertions. If you're not using ExUnit, you'll probably want to override this default by calling use WhiteBread.Context, test_library: :some_other_library_name.

At the moment, the only library names available are :ex_unit (same as the default), :espec, and nil (which skips the test library setup step altogether).

Next steps - Additional Suites and subcontexts

After following the getting started steps you may find your default context starts to get a bit large. There are two ways this can be broken apart:

  1. By composing your default suite out of subcontexts using the import_steps_from macro.
  2. By splitting your features into different suites each starting with a different context.


Sub contexts allow the step definitions of multiple contexts to be imported in to a parent context. The parent context defines all the start and stop callbacks but all the steps in the child context will be available.

defmodule WhiteBread.Example.DefaultContext do
  use WhiteBread.Context

  import_steps_from WhiteBread.Example.SharedContext

  # Rest of the context here as usual

Multiple suites

Defining suites allows you to use a different starting context for groups of features. This will often be along the lines of a bounded context. You can also run one feature multiple times under different contexts. This is especially useful if you have a few different ways of accessing your software (web, rest api, command line etc.).

Suite configuration is loaded from features/config.exs. An example with multiple suites is:

defmodule WhiteBread.Example.Config do
  use WhiteBread.SuiteConfiguration

  suite name:          "Default",
        context:       WhiteBread.Example.DefaultContext,
        feature_paths: ["features/sub_dir_one"]

  suite name:          "Alternate",
        context:       WhiteBread.Example.AlternateContext,
        feature_paths: ["features/sub_dir_two"]

  suite name:          "Alternate - Songs",
        context:       WhiteBread.Example.AlternateContext,
        feature_paths: ["features/sub_dir_one"],
        tags:          ["songs"]

Each suite gets run loading all the features in the given paths and running them using the specified context. Additionally the scenarios can be filtered to specific tags.

Suites: Context per feature

This is part of the Suite Configuration and it automatically maps a .feature with a context module file automatically.

It is also possible to run this with additional manually defined suites.


defmodule WhiteBread.Example.Config do
  use WhiteBread.SuiteConfiguration

  context_per_feature namespace_prefix: WhiteBread.Example,
                      entry_path: "features/context_per_feature"

  # Extra config can also be provided to apply to each generated suite                      
  context_per_feature namespace_prefix: WhiteBread.Example,
                      entry_path: "features/context_per_feature",
                      extra: [
                        tags: ['special']

  suite name:          "Alternate",
        context:       WhiteBread.Example.AlternateContext,
        feature_paths: ["features/sub_dir_two"]

About the context_per_feature configuration:

  • namespace_prefix: the namespace your modules will start with. The file name of the feature will be converted into a module name and appended to the end of the namespace_prefix e.g. my_new_sandwich.feature to WhiteBread.Example.MyNewSandwichContext
  • entry_path: the location of your feature files.

note: context files need to be added to your features/contexts folder still.

Speeding things up - async running

More than likely you have a multicore machine. To get things going a little faster each suite can be configured to run all features and scenarios in a separate process.

This can be done by setting run_async to true on any suite:

defmodule WhiteBread.Example.Config do
  use WhiteBread.SuiteConfiguration

  suite name:          "Speedy run",
        context:       WhiteBread.Example.DefaultContext,
        feature_paths: ["features/sub_dir_one"],
        run_async:     true

note: At the moment each suite will be run sequentially in the order they appear in the config file.

Speeding things up - timeouts

By default each scenario gets 30 seconds to execute. After which point it will fail with a timeout warning. Each context can define a custom timeout function:

defmodule WhiteBread.Example.DefaultContext do
  use WhiteBread.Context
  scenario_timeouts fn _feature, scenario ->
    case scenario.name do
      "possible slow scenario" -> 60_000
      _               -> 5000

  # Rest of the context here as usual

This function gets the full structs representing the feature and scenario being executed so it's possible to base the decision to change the timeout on any available property: tags, name, description etc.

HTML Output (and other outputs)

For HTML reports configure WhiteBread (e.g. in config.exs) with the HTML outputer and optionally a file name for the document:

JSON reports are also available.

config :white_bread,
  outputers: [{WhiteBread.Outputers.Console, []},
              {WhiteBread.Outputers.HTML, path: "~/build/whitebread_report.html"},
              {WhiteBread.Outputers.JSON, path: "~/build/whitebread_report.json"}

Public interface and BC breaks

The public interface of this library covers:

  • The exported mix command: mix white_bread.run
  • The WhiteBread and WhiteBread.Helpers modules.
  • The macros exported by the WhiteBread.Context module.
  • The ContextBehaviour defined in WhiteBread.ContextBehaviour.
  • The config.exs structure and the macros exported by the WhiteBread.SuiteConfiguration module.
  • The structures defined in WhiteBread.Gherkin.
  • The location of feature and context files loaded automatically.
  • The messages that custom outputers receive (documented in WhiteBread.Outputer)

Any changes outside of the above will not be considered a BC break. Although every effort will be made to not introduce unnecessary change in any other area.


Contributions more than welcome but please raise an issue first to discuss any large changes.